Plants experience stress competing for water with neighboring plants, both with members of the same species (intraspecific competition) and different species (interspecific competition). As plants conduct photosynthesis, they open pores in their leaves called stomata to uptake carbon dioxide from the atmosphere. However, there is a tradeoff: as carbon is gained, water is lost through evaporation as stomata open during the transpiration process. This tradeoff—the carbon gain to water lost during photosynthesis—represents the plant’s water use efficiency. Plant physiological stress due to external factors may affect stomatal regulation and water use efficiency. Through two experiments, one in a controlled growth chamber and the other in the natural area of Red Butte Garden, this study analyzes the differences in water use efficiency of native Utah plant species (Populus tremuloides, Quercus gambelii, Acer grandidentatum and Acer negundo) as they face differing levels of interspecific and intraspecific competition. Plant water use efficiency decreased when plants experienced intraspecific competition, and further study is needed to assess the impact of interspecific competition on plant water use efficiency. Understanding the correlation between competition and water use efficiency will help predict future plant and forest success not only to stressors such as competition, but also to changing water availability resulting from global climate change.
